1. Field of the Invention
The present invention relates to speed reducing mechanisms, drive devices, and optical instruments.
2. Description of the Related Art
There is known a blade drive device as a drive device used in a camera. The blade drive device, for example, includes: a board including an opening; a blade adjusting the aperture of the opening; a drive ring for driving the blade. The drive ring is driven by receiving the drive force from an actuator. The driving of the drive ring causes the blade to drive, so that the aperture of the opening formed on the board is adjusted (See Japanese Unexamined Patent Publication No. 9-50065).
In the drive device disclosed in Patent Document 1, the drive force of the actuator is transmitted to the drive ring via plural decelerating gears. In this way, by using a reduction gear having the plural decelerating gears through which the drive force is transmitted, the accuracy of the stop position of the drive ring can be improved. The accuracy of the stop position of the drive ring is improved, thereby improving the accuracy of the position of the blade and the accuracy of adjusting the aperture of the opening.
However, since the drive device having such a speed reducing mechanism has plural decelerating gears which are meshed with each other, the operational noise is increased. Also, since the plural decelerating gears are overlapped in the optical axis direction, the space in the optical axis direction is necessary, and the number of the parts and the manufacturing cost are increased.